Gear transmission, whether for automotive vehicle purposes or other load-driving purposes can be provided between a prime member, such as an internal-combustion engine, and a load such as a power train or wheel-driving system of the vehicle.
Such transmissions can be simple or intricate, but almost invariably will comprise a housing, an input shaft connected to the prime mover, an output shaft connected to the load, and a drive train within the housing for selectively coupling the input shaft to the output shaft with various transmission ratios, depending upon which of the gears of the drive train are in mesh with one another at a particular point in time.
Shifting may be effected by intermediate or other gears of the drive train, by shifting forks or the like, or planetary gearing may be employed in the drive train with individual members of the planetary gear systems being coupled together, immobilized or rendered free-wheeling by clutches or brakes, or various gears of the drive train may be coupled to each other or to various shafts by suitable clutches, all depending upon the complexity, the number of transmission ratio steps or ranges desired, etc.
Almost invariably, however, such transmissions include a reversing system whereby, upon actuation of the system, the sense of rotation of the output shaft can be reversed.
The present description is concerned with a reversing system of the type in which the drive train includes at least one drive gear, a reversing gear is provided in the housing and is coupled with the output shaft, e.g. by being fixed thereto, and the reversing system includes a sliding gear which is axially shiftable on a fixed shaft in the housing, while being in mesh with the driving gear so as to engage (mesh with) the reversing gear or disengage from the latter depending upon operation of a reversing continuity such as a fork adapted to shift the slidable gear.
Since the slidable gear is coupled with the drive gear substantially continuously, it is in rotation whenever the drive gear is rotated. Obviously the engagement of a rapidly rotating sliding gear with a stationary reversing gear will pose a problem.
There has thus been proposed (see German patent document-open Application DE-OS No. 27 51 699) a device which is capable of decelerating the sliding wheel, thereby coupling same to engage simply, reliably, quickly and quietly with the reversing gear.
In other words, the decelerating device is designed to reduce the speed or halt the rotation of the sliding gear so that it is practically at standstill when shifted into mesh with the reversing gear.
It is also known to provide, in addition to the decelerating or brake device for the sliding gear, a locking device which operates similarly to a so-called locking synchronization. Such device can be of the ratchet type.
While the system of this reference does not directly connect the sliding gear or wheel continuously with the drive gear or wheel but rather interposes a clutch, it is apparent that the sliding wheel can simply be lengthened to permit continuous drive.
The system of the reference operates reliably and quietly as long as the sliding wheel is at standstill when it engages the ratchet wheel. This condition is generally ensured by the locking device. Nevertheless it is possible to attempt to engage the reversed gear while the vehicle is still in significant motion since deceleration of the sliding wheel cancels out the effect of the locking device. As a result, jerks, shocks or like can be imparted to the drive line or train and the output shaft with concomitant damage to the gear wheels.